Aircraft landing gear warning signal



July 26, 1955 J. w. TEEGARDEN AIRCRAFT LANDING GEAR WARNING SIGNAL Filed April 21, 1955 MM QN FIND. o G W\ \N R b S wwtzuwk QR U6 6 NuwSQm z: WW4

United States Patent AIRCRAFT LANDING GEAR WARNING SIGNAL 7 John W. Teegarden, Dayton, Ohio Application April 21, 1955, Serial No. 350,272 Claims. (Cl. 340-27 (Granted under Title 35, U. S. Code (1952),sec. 266) The invention described in the foregoing specificationand claims may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to aircraft landing gear warning systems and more particularly to a landing gear warning system of the audible type..

In the art of landing gear warning systems it is common practice to employ a switch which is actuated when the landing gear of the airplane is not in the down position and the air speed is below a predetermined value. In such systems the switch is employed tocomplete an energizing circuit of an electrical signal device which may be of either the visual or audible type.

In the event that the signal device is of the visual type, it has been found that the pilots attention to other matters preliminary to the landing operation might prevent him from seeingthe signal and, therefore, he might not be warned of the perilous condition. In the event that the signal was of the audible type, it was the usual practice to mount the buzzer or horn in close vicinity to the pilot, however, since the pilot might well be listening to by means of the switch to the earphones of one or more .t

of the occupants of the aircraft.

An object of this invention is to provide an airplane landing gear warning system which will be more reliable and less expensive than the previously known warning systems.

The above object, as well as other objects, features and advantages of this invention will be more fully understood in view of the following description when taken in conjunction with the drawing, wherein the single figure is a simplified schematic drawing of a landing gear warning system constructed in accordance with the principles of this invention.

Referring now to the drawing, electrical oscillations of audio frequency are produced by the first section of tube V1 which includes anode 1, cathode 2, and grids 3 and 4 and the circuit associated with that section of tube V1 which circuit includes transformer T1, capacitor C1, resistor R1 and a suitable source of D. C. potential 5. Since the usual source of D. C. potential in an airplane is 28 volts, it is desirable that the tube V1 be of the type 28D7'which is designed to operate on 28 volts plate supply. The electrical oscillations are applied to grid 6 of the second section of tube V1. The second section of tube V1 which includes grids 6 and 7, anode 8 and cathode 9 together with the circuit associated with that section of tube V1 form a conventional amplifier circuit.

The amplified audio signal which appears across the secondary winding of transformer T2 will appear across outnot in the down position and the speed of the aircraft is 7 below a predetermined value.

The earphones 21 are energized from terminals 10 and 11 over suitable conductors 19 and 20 which are shown as dotted lines in the drawing to indicate that it is not necessarily a single circuit connection, that is, the earphones 21 may be connected to the aircraft radio or interphone systems but, nevertheless, the terminals 10 and 11 are also connected to those earphones. That connection may well be through the usual control box which permits the earphones to be connected to either the aircraft radio or the interphone system.

A suitable attenuator including resistors R4 and R5 is preferably provided in the output circuit in order to permit the magnitude of the warning signal to be adjusted to the desired level.

In operation, when the aircraft landing is not in the down position and the aircraft speed is below a predetermined value, switch S2 closes energizing winding 18 of relay 14. When the relay is energized, contacts 12 and 13 are closed and contacts 15 and 16 are open, this causes audio frequency signals to be applied to the earphones 21. The opening of contacts 15 and 16 breaks the energizing circuit of relay coil 18, however, due to capacitor C4, the coil 18 will remain energized for a period of time determined by the discharge time of capacitor C4 and its discharge circuit which includes coil 18 after which time the bias spring 17 will cause the relay to return to its normal position. After a short delay following closure of contacts 15--16, depending upon the charging time of condenser C4, the relay is again actuated. This cycle is repeated as long as switch S2 is closed. This cyclic operation of relay 14 will cause an intermittent audio signal to be applied to earphones 21.

In a preferred embodiment of this invention, the values of the circuit elements are as follows:

Tube V1 type 28D7 Capacitor C1 .003 mfd. Capacitor C2 .01 mfd. Capacitor C3", 1.0 mfd. Capacitor C4 250 mfd./25 w. v. Resistor R1 100,000 ohms Resistor R2 -1 560,000 ohms Resistor R3 ohms/5 w. Resistor R4 5,000 ohms Resistor R5 2,000 ohms Although particular values have been shown for the various circuit elements of the drawing and although the drawing and description have illustrated a particular circuit embodying the principles of this invention, it will be understood that many additions, omissions and modifications may be made without departing from the spirit and scope of this invention.

What is claimed is:

1. A landing gear warning device for use in aircraft in which means are provided for closing a first electric circuit whenever the air speed falls below a predetermined minimum with the landing gear not fully extended, said device comprising a source of audio .frequency electrical oscillations, an output circuit for said source of audio frequency electrical oscillations, normally open electrical contacts in said output circuit means for causing said normally open contacts in said output circuit 'to cyclically open and close when said first electric circuit is closed. v

2. A landing gear warning device for use in aircraft in which means are provided for closing a first electric circuit whenever the air speed falls below a predetermined minimum with the landing gear not fully extended, said device comprising a source of audio frequency electrical oscillations, an output circuit for said source of audio frequency electrical oscillations, first normally open electrical contacts in said output circuit, a relay coil for operating said first normally open electrical contacts to closed position, an energizing circuit for said relaycoil including first normally closed electrical contacts and second normally open electrical contacts in said first electric circuit, said secondnormally open electrical contacts being adapted to be operated by said first electric circuit closing means, means responsive to the energizing of said relay coil to cause said first normally closed electrical contacts to be operated to open position and means responsive to the energizing of said relay coil to cause said relay coil to remain energized for a predetermined length of time.

3. A landing gear warning device for use in aircraft. n

in which means are provided for closing a first electric circuit whenever the air speed falls below a predetermined minimum with the landing gear not fully extended, said device comprising a source of audio. frequency electrical oscillations, an output circuit for said source of audio frequency electrical oscillations, an earphone in said output circuit responsive to said audio; frequency electrical oscillations to produce sound when energized thereby, normally open contacts in said output circuit and means operated when said first electric circuit is closed to cause said normally open contacts to cyclically open and close.

4. A landing gear warning device for use in aircraft in which means are provided for closing a first electric circuit whenever the air speed falls below a predetermined minimum with the landing gear not fully extended, said device comprising a source of audio frequencyelectrical oscillations, an output circuit for said source of audio frequency electrical oscillations, first normally open contacts in said output circuit, an earphone in said output circuit responsive to said audio frequency electrical oscillations when said first normally open contacts are closed to produce sound, a relay coil for operating said first normally open electrical contacts to closed position, an energizing circuit for said relay coil including first normally closed electrical contacts and second ynormally open electrical contacts in said first electrical circuit, said second normally open electrical contacts be ing adapted to be operated by said first electric circuit closing means, means responsive to the energizing of said relay coil to cause said first normally closed electrical contacts to be operated to open position and means responsive to the energizing of said relay coil to cause said relay coil to: remain energized for a predetermined length of time. i

S. A'landing gear warning device for use in aircraft in which means are provided for closing an electric circuit Whenever the air speed falls below a predetermined minimurn'witlithe landing gear not fully extended, said device comprising a source of audio frequency, means for inserting a signal into the audio system of the aircraft radio, a-relay having a coil, a set of normally closed contacts and a set of normally open contacts, an energizing circuit forsa-id rela-y comprising a source of voltage, said circuit closing means,- said normally closed contacts and said coil connected in series, means for connecting said source of audio frequency to said inserting means through the normally open contacts of said relay, and means for delaying the actuation of said relay when said energizing circuit is closed and for delaying the release of said relay when said energizing circuit is opened.

ReferencesCitedin the file of this patent UNITED STATES PATENTS 2,051,827 De Florez Aug. 25, 1936 2,11 5,70.-l Baeret a1. May 3, 1938 2,116,960 Brown et al. May 10, 1938 2,288,204 Qstlund et a1. June 30, 1942 2,395,368 Bull Feb. 19, 1946 

